The present invention relates to an electrode binder composition, an electrode slurry that includes the binder composition and an electrode active material, an electrode that is produced by applying the slurry to a collector, and drying the slurry, and an electrical storage device that includes the electrode.
In recent years, a high-voltage electrical storage device having a high energy density has been desired as a power supply for driving an electronic instrument. In particular, a lithium-ion battery or a lithium-ion capacitor is expected to be a high-voltage electrical storage device having a high energy density.
An electrode used for such an electrical storage device is produced by applying a mixture of an electrode active material and polymer particles that function as a binder to the surface of a collector, and drying the mixture. The polymer particles are required to exhibit a capability of binding the electrode active material, a capability of binding the electrode active material and the collector, scratch resistance when winding the electrode, and powder fall resistance (i.e., a fine powder of the electrode active material or the like does not occur from an electrode composition layer (hereinafter may be referred to as “electrode active material layer”) due to cutting or the like). If the polymer particles satisfy these properties, it is possible to produce an electrical storage device that has high flexibility in structural design (e.g., an electrode folding method or an electrode winding radius), and can be reduced in size. It was found that a capability of binding the electrode active material, a capability of binding the electrode active material and the collector, and the powder fall resistance have an almost proportional relationship. Therefore, these properties may be comprehensively referred to as “adhesion”.
When producing a positive electrode, it is advantageous to use a fluorine-containing organic polymer (e.g., polyvinylidene fluoride) that exhibits slightly poor adhesion, but exhibits excellent oxidation resistance. When producing a negative electrode, it is advantageous to use a (meth)acrylic acid polymer that exhibits slightly poor oxidation resistance, but exhibits excellent adhesion.
Various techniques have been studied and proposed in order to improve the properties (e.g., oxidation resistance and adhesion) of a polymer that is used for the electrode binder. For example, JP-A-2011-3529 proposes a technique that provides a negative electrode binder with oxidation resistance and adhesion by utilizing polyvinylidene fluoride and a rubber polymer in combination. JP-A-2010-55847 proposes a technique that improves adhesion by dissolving polyvinylidene fluoride in a specific organic solvent, applying the solution to the surface of a collector, and removing the organic solvent at a low temperature. JP-A-2002-42819 proposes a technique that improves adhesion by utilizing an electrode binder having a structure that includes a main chain formed of a vinylidene fluoride copolymer and a side chain that includes a fluorine atom.
A technique that improves the above properties by controlling the composition of a binder (see JP-A-2000-299109), and a technique that improves the above properties by controlling the amount of 2,4-diphenyl-4-methyl-1-pentene that remains in particles when polymerizing latex (see JP-A-2002-319402), have also been proposed.